This invention relates to improvements in video image processing systems particularly those which include the combination of two or more incoming video signals under the control of a control signal.
Three prior art systems for this type of processing are shown in FIGS. 1-3. Although the processing is carried out in a similar manner by all three the inputs and outputs of each system are different.
In video graphics equipment there are two requirements that can be met by this type of processor, the need to produce new images under operator control to give the effect of painting and to combine signals from two or more sources of image signals so that the output image can contain areas of image signals from one or all the sources. The circuit shown in FIG. 1 is a so-called brush processor, described in Ser. No. 326,293 (which is incorporated herein by reference), used in Quantel's video graphic system to create new images. In this system the image is produced by combining new video signals representing luminance or chrominance with signals stored in a framestore in proportions determined by a control signal K. The luminance and chrominance signals to be used are chosen by the operator as is also the notional artists implement to be used in the creation. Command signals can be input to the system by the operator by the use of a stylus and touch tablet to identify image points at which `paint` is to be `applied`. The control signal K for each identified image point is produced at the output of multiplier 2 in FIG. 1 and results from the multiplication of first a brush signal, which is a signal relating to the distribution power of the notional implement chosen by the operator, second a signal relating to the pressure applied by the operator to the stylus and third a stencil signal. The operation of a stencil in this system is analogous to that in the conventional artists equipment. Where the operator has not chosen to use a stencil this signal will be set to 1 and so K will be simply brush signal times pressure. K will always be a value between 0 and 1. The processing is done picture point by picture point but K may be precalculated for each picture point as described in co-pending U.S. application Ser. No. 851,110, however this will not effect the operation of this circuit.
Referring only to luminance signals, although similar processing is applied to chrominance signals, the output is produced by multiplying the incoming luminance chosen by the operator by K in multiplier 3 and adding this to the luminance times 1-K in 5. The luminance applied to 5 is the luminance generated for the particular picture point from previous operations of the system. It will be obvious that the output is then K L in +(1-K) L store, where L in is the incoming luminance and L store is the luminance stored at that point. It is found that this processing gives a very realistic image.
FIG. 2 shows a processor which can combine two picture sources in a way which produces an output image which contains different areas of each image as described in U.S. application Ser. No. 457,098 (which is incorporated herein by reference). Where one image is moved relative to the second, parts of the that image may be made to appear as they move in front of objects in the stationary image. Each picture source is provided with a stencil signal which consists of signals for each picture point having a value between 0 and 1 and these signals are multiplied together to provide a control signal k at the output of multiplier 7. The control signal k is again a digital signal with a value between 0 and 1 and is used to determine the proportions in which the two picture signals are combined. It is to be understood that in this system also separate processing paths will be provided for luminance and chrominance signals. In this system, means are provided for displacing one set of the picture signals, and the corresponding stencil signals, relative to the other set, and for allowing part of one image to be moved around a second image by the operator until the correct position is found when the composite image can then be processed to be part of the final image.
The output from adder 11 in FIG. 2 is kP1+(1-k) P2 where P1 is a signal from the first picture source and P2 is a signal from the second picture source. The circuit components needed to achieve this are the same components as in 2 to 6 FIG. 1 arrangement but the circuits are not usually combined. By calculating the stencil signals for each picture source it can be provided that where those areas in picture 1 are to appear on the output image k will be large and vice versa, where picture 2 is to appear. Additional circuitry is of course provided to produce the addressing and to move one picture relative to the second.
The prior art system shown in FIG. 3 is a processor used in still store systems which may be part of a video graphics system. In these systems one facility that is desirable is to be able to view the contents of one store and at the same time preview the contents of a second store and to be able to cut or fade from one to the other. The control value K in the processing in this case can be used then to achieve fade by gradually changing from 1 to 0 or cut by changing more abruptly. Two still pictures are stored in framestores 12 and 13 and then output to the multipliers 14-17. The factor K is applied as a second input to multipliers 15 and 16 and 1-K to multiplier 14 and 17 and it will be obvious from FIG. 3 that the main output from 20 consists of KP2 +(1-K) P1, and the preview output from 19 consists of KP1, +(1-K) P2. As K changes from 0 to 1 then the image stored in framestore 12 will disappear at the main output from 20 and reappear at the preview output from 19. All three circuits described operate on a point by point basis and with suitable additional components can provide a displayed image.
Although the components used in these prior art systems are well known, the implementation of these processors in hardware can be very costly. The processor for the still store is rather more expensive than the other two because of the large number of multipliers involved.